1. Field of the Invention
This invention relates to a control system and method for an internal combustion engine, such as a diesel engine, that injects fuel into a combustion chamber during the expansion stroke or the exhaust stroke.
2. Description of the Related Art
Conventionally, this kind of control system for a diesel engine is disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 2003-269230. This diesel engine (hereinafter referred to as “the engine”) has a swirl control valve disposed in an intake pipe, for producing a swirl in the combustion chamber, and a filter disposed in an exhaust pipe, for collecting particulates contained in exhaust gases. The control system not only injects fuel necessary for combustion of the engine, but also executes post injection in which fuel is injected into the combustion chamber during the expansion stroke or the exhaust stroke, as required. The post injection causes unburned fuel to be contained in exhaust gases, and then be burned e.g. at a filter, to thereby increase the temperature of the filer to burn PM deposited on the filter, whereby the filter is regenerated.
Further, when such post injection is executed, part of fuel subjected to post injection during the exhaust stroke attaches to the cylinder wall without being exhausted form the combustion chamber, and the attached fuel is mixed into the engine oil to cause oil dilution. To overcome this problem, the conventional control system controls the swirl control valve during execution of post injection to produce a swirl, whereby atomization of fuel supplied by post injection is accelerated to thereby suppress attachment of fuel to the cylinder wall.
As described above, the conventional control system produces a swirl when executing post injection. The swirl is, however, produced in a manner caused by the suction operation of the engine. Therefore, during the expansion stroke and exhaust stroke in which post injection is executed after the suction operation of the engine, the swirl diminishes, which prevents sufficient atomization of fuel supplied by post injection, and hence oil dilution cannot be necessarily prevented. Therefore, there is a fear that the function of engine oil, such as lubrication of the engine, cannot be maintained.